1. Field of the Invention
The present invention relates to electro-optical devices for emitting light radiation from a semiconductor medium which is subjected to controlled energy excitation.
2. Description of Related Art
Electro-optical semiconductor devices, for example light-emitting diodes (LEDs), semiconductor lasers, etc., have become widespread over the last few years. This is true, in particular, of lasers suitable for use in optical fiber telecommunications.
One of the problems which arises is developing lasers suitable for emitting in the transparency range of the optical fibers used. Thus, the use of silica based optical fibers requires lasers which emit in the infrared over a range of wavelengths extending from 1.3 .mu.m to 1.7 .mu.m.
The first semiconductor lasers were made with samples of gallium arsenide GaAs. However, the conditions required for obtaining a laser effect were particularly Draconian since the effect could only be obtained at a very low temperature using pulses at a very low repetition rate.
GaAs lasers have since been made to operate continuously and at ambient temperature, but at the price of using complex and heterogeneous structures which are known as "heterojunctions".
In addition to being complex in structure, it should be observed that GaAs lasers suffer from the major drawback of not emitting in the transparency range of optical fibers (1.3 .mu.m to 1.7 .mu.m). Conventional GaAs lasers emit at a wavelength of about 0.9 .mu.m which corresponds to emission at the band edge of the material, i.e. at the transition of the forbidden band situated between the conduction band and the valence band.
Quaternary GaInAsP lasers are also known, and they emit around 1.5 .mu.m, however the semiconductor material must then be associated with a substrate such as an InP substrate.